1. Field of the Invention
The present invention relates to a photosensitive recording material, a photosensitive planographic printing plate precursor, and stacks thereof. In particular, the present invention relates to a photosensitive recording material suitable for a negative planographic printing plate precursor capable of direct drawing with a laser light and high speed processing. More particularly, the present invention relates to a photosensitive recording material improved in adhesiveness between the recording materials even by stacking plural sheets of the photosensitive recording material, and a planographic printing plate precursor using the photosensitive recording material.
2. Description of the Related Art
Conventionally, a plate having a lipophilic photosensitive resin layer provided on a hydrophilic support has been used widely as a planographic printing plate precursor, and a desired printing plate is obtained by a plate-making method which usually involves masked light exposure (surface light exposure) via a lithographic film and then removing a non-image area by dissolution. In recent years, digitalization techniques which involve electronic processing, accumulation and output of image information with a computer are spreading. A wide variety of new image output systems compatible with these digitalization techniques have come to be used in practice. As a result, there has been demand for computer-to-plate (CTP) techniques for producing a printing plate directly by scanning a highly directional light such as a laser light according to digitalized image information without a lithographic film, and the provision of a planographic printing plate precursor adapted to these techniques has proved a significant technical challenge.
As a planographic printing plate precursor capable of such scanning exposure, a planographic printing plate precursor including a hydrophilic support provided thereon with a lipophilic photosensitive resin layer (hereinafter, sometimes referred to as “photosensitive layer”) containing a photosensitive compound capable of generating active species such as radicals or Brønsted acid upon exposure to a laser light has been proposed and made commercially available. This planographic printing plate precursor is subjected to laser scanning according to digital information to generate active species acting on the photosensitive layer to cause physical or chemical change, thus making the layer insoluble, and then subjected to development treatment to give a negative planographic printing plate.
In particular, a planographic printing plate precursor provided with a photopolymerizable type photosensitive layer containing a photopolymerization initiator superior in photosensitive speed, an addition polymerizable ethylenic unsaturated compound and a binder polymer soluble in an alkali developing solution on a hydrophilic support and, as required, a protective layer having oxygen blocking property on a hydrophilic support has the advantages of high productivity, simple development treatment and high resolution and print adhesion, which advantages give the planographic printing plate precursor a desirable printing performance (see for example, Japanese Patent Application Laid-Open (JP-A) No. 10-228109).
Further, a planographic printing plate precursor has been disclosed which includes a photopolymerizable photosensitive layer containing a photopolymerization initiator, an ethylenically unsaturated compound capable of addition polymerization, and a binder polymer soluble in an alkaline developer and having a repeating unit of a specified structure on a hydrophilic support and, as required, a protective layer having oxygen blocking property on a hydrophilic support (see, for example JP-A 2004-318053). Further, a negative planographic printing plate precursor has been disclosed which includes a photopolymerizable photosensitive layer, and an oxygen blocking protective layer containing an inorganic lamellar compound on a hydrophilic support (see, for example JP-A No. 11-38633).
Also, in order to further improve productivity, that is, to enhance plate making speed, a recording material which employs a photopolymerizable composition containing a cyanine dye having a specific structure, an iodonium salt and an addition polymerizable compound having an ethylenic unsaturated double bond in a photosensitive layer and needs no heating treatment after imagewise exposure (see, for example, Japanese Patent Application Publication (JP-B) No. 7-103171). This image recording material, however, has a drawback in that polymerization inhibition is caused by oxygen in the air in the polymerization reaction, bringing about reduced sensitivity and unsatisfactory strength of the formed image.
To address this problem, the following methods are known: a method in which a protective layer containing a water-soluble polymer is formed on a photosensitive layer and a method in which a protective layer containing an inorganic lamellar compound and a water-soluble polymer is formed (see, for example, JP-A No. 11-38633). The presence of the protective layer prevents polymerization inhibition so that a curing reaction is promoted at the photosensitive layer and it is therefore possible to improve the strength of the image area.
Meanwhile, with regard to productivity in the plate-making operation of a photopolymerization type planographic printing plate precursor featuring a simple development treatment, it is important to shorten the time required in the exposure process.
In the exposure process, a planographic printing plate precursor is usually supplied as a stack of the planographic printing plate precursors in which an interleaf sheet is inserted between each of the planographic printing plate precursors. The interleaf sheet has a function for preventing the planographic printing plate precursors from adhering to one another, and a function for preventing the surface of a relatively soft protective layer from being damaged by being rubbed with an aluminum support. However, the time necessary for removing the interleaf sheet in the exposure process has been the cause of inefficiency in plate-making. The process for removing the interleaf sheet may be omitted by using a stack having no inserted interleaf sheet between the planographic printing plate precursors, in order to make the exposure process more efficient. However, the problems of adhesion of the planographic printing plate precursor and damage of the surface of the protective layer provided on the photosensitive layer by rubbing with the back face of the aluminum support need to be addressed when a stack having no inserted interleaf sheet is used.
When a photosensitive planographic printing plate precursor is manipulated under room light, unintended fogging due to long term exposure to the room light having lower luminance than laser exposure (safety light fogging in visible light sensitive materials; referred to as “safety light fogging” hereinafter when appropriate) may be caused. In order to prevent this problem from occurring, radical species generated unintentionally are quenched by controlling oxygen permeability of the protective layer by a known method. Specifically, a method in which a protective layer including at least one of polyvinyl pyrrolidone and a copolymer of polyvinyl pyrrolidone and vinyl acetate is formed, and the mass of the protective layer is controlled to within a range of from 0.50 g/m2 to 2.30 g/m2 has been proposed (see, JP-A2005-121863).
As described above, there has been a need for a photosensitive recording material, and particularly a photosensitive planographic printing plate precursor, which is capable of suppressing polymerization inhibition of the photosensitive layer, does not require insertion of interleaf sheets when a plurality of planographic printing plate precursors are stacked, and is capable of improving productivity of plate making operations. However, such a photosensitive recording material and a planographic printing plate precursor have not yet been provided.